[Sjoerd]

To compensate for the US emissions of CO2 equivalent, you would need to create in the order of 4 cubic kilometers of charcoal every year. You could cover the whole of California with a layer of 1 centimeter (about half an inch) of charcoal every year.

So turning trees into charcoal scales up to a certain point, but not to the point that it "would even remotely make a difference for climate change", as OP said.

[adrianN]

Yeah that sound about right given that we’ve burned enough coal already to lower whole regions by dozens of meters.